Question

below is a code i have been working on, but i keep run-inning in to trouble

Answer 1

#include <iostream>
#include <ctime>
#include <iomanip>

using namespace std;

int main(){
int n;
cout << "Enter a number: ";
cin>>n;
double m[100][100];
for (int r=0;r<n;r++){for (int c=0;c<n+1;c++){
m[r][c]=1+rand()%9;}
}
for (int r=0;r<n;r++){for (int c=0;c<n+1;c++){
cout<<m[r][c]<<" ";}cout<<endl;
for(int p=0;p<n+1;p++){
for (int i=0; i<n+1;i++){
m[r][i]/=m[r][p];}}
}
cout<<endl;

for (int r=0;r<n;r++){for (int c=0;c<n+1;c++){
cout << setprecision(3)<<m[r][c]<<"\t";}cout<<endl;
}
return 0;
}

Answer 2

i can't get this part
for(int p=0;p<n+1;p++){
for (int i=0; i<n+1;i++){
m[r][i]/=m[r][p];}}
to divide the row by the first column number for ever column

Answer 3

@e.mccormick this is program is the linear program that u have helped me before, and this is wat i came up with, but i get stuck on dividing.
Also how do i subtract the one column by another with in a loop
i tried doing it but i get stuck.
please help

Answer 4

Did you try tossing a little test print in there to see what the m[r][i] and m[r][p] are?

Answer 5

m[r][i] and m[r][p] carries the row and the column, it should divide the rows by the first number of each column, but it doesn't just do that,; it does other things also

Answer 6

Yes, but I am saying if it is not doing what you expect, it is time to see what values are going in and coming out.

Answer 7

when i replace the p with numbers, i kinda get the right values but it only calculates that first row column and the ones before it..
idk if what im saying makes sense

Answer 8

One thing that can help is a test harness. That is, you make a matrix you know what it will do when as it runs through the code. Once you have worked out, perhaps even tested in a matrix solver. Then you can try the other code against it easier because you will know what that should do at that moment. Then looking at what is really happening is easier because the values are known.

Answer 9

@e.mccormick i tried different way, but instead of the first columns being divided, it is the last row being divided, here is the new one.. it would be nice if u tell me what i should change or switch, so i can start doing the other problem
for(int p=0;p<n;p++){
for (int i=0; i<n+1;i++){
m[r][i]/=m[p][i];}}

Answer 10

Well, without making a matrix that I know how to work, it is kind of going in blind. I have been looking for a good worked example that would make use of fracrtions, and therefore be useful in this program. Did not have much luck.

On this page:
http://www.wyzant.com/resources/lessons/math/precalculus/systems_of_equations/matrix_method

They start by talking about the process. Same basic thing I went over with you. But about half way down they have a nice system of 3 equations that makes a 3x4 matrix that solves to \(\{x,y,z\} = \{1,-2,1\}\). Because they have steps and a solution, it can be used as a way to make a test matrix in the software and see what happnes.

Answer 11

@wio im trying to divide and multiply matrix like the example e.mccormick showed above, but i keep getting wrong answers, here is the code that i revised
for(int i =0; i<n+1;i++){
m[r][i]= ((1/m[r][i]))*m[0][i];
}}
can u help

Answer 12

Hmmm

Answer 13

Can you create a new function for it?

Answer 14

Lol, why don't tap stuff and put loops on multiple lines?

Answer 15

Are you doing matrix multiplication?

Answer 16

i can create a new function, i just wanted to fix up the math part first.
i am doing linear algebra matrix to find the solutions for x,y and z

Answer 17

What is the problem currently then?

Answer 18

int main(){
int n;
cout << "Enter a number: ";
cin>>n;
double m[100][100];
for (int r=0;r<n;r++){for (int c=0;c<n+1;c++){
m[r][c]=1+rand()%9;}
}
for (int r=0;r<n;r++){for (int c=0;c<n+1;c++){
cout<<m[r][c]<<" ";}cout<<endl;
for(int i =0; i<n+1;i++){
m[r][i]= ((1/m[r][i]))*m[0][i];
}}
cout<<endl;

for (int r=0;r<n;r++){for (int c=0;c<n+1;c++){
cout << setprecision(3)<<m[r][c]<<"\t";}cout<<endl;
}
return 0;
}
this is the current program, im trying to divide the first row by the first row column numbers

Answer 19

Okay make a function for any particular column.

Answer 20

```
void divideColumn(double m[100][100], int n, int col, double val) {
int i;
for (i = 0; i < n; i++) {
m[col][i] /= val;
}
}

```

Answer 21

Hold on, let me double check.

Answer 22

Try this
```
void divideColumn(double m[100][100], int n, int c, double val) {
int i;
for (i = 0; i < n; i++) {
m[i][c] /= val;
}
}
```

Answer 23

Then do to the first column by the first number, say
```
divideColumn(m, n, 0, m[0][0]);
```
Using `0` since it is 0 based.

Answer 24

Do you get it?

Answer 25

i got it, the math works, but im suppose to divide the row not the columns, so do u thing it would would work if i do this
void dividerow(double m[100][100], int n, int r, double val) {
int i;
for (i = 0; i < n+1; i++) {
m[r][i] /= val;
}
}
instead since im dividing the rows.

Answer 26

Yeah, I think so.
But why are you goint up to n+1?

Answer 27

+1 creats the solution for x , y and z, the last row is the solution and once the could is complete it needs to look like this
1 0 0 | 34
0 1 0 | 45
0 0 1 | 32

something like that

Answer 28

Ok

Answer 29

Thank alot for ur help

Answer 30

Don't divide by 0

Answer 31

i won't. i will have an if statement for that

Answer 32

@e.mccormick Thanks

Answer 33

Yah, he is building a matrix solver.